1. Field of the Invention
The present invention relates to a fuser configured to pass and fuse a recording material with an unfixed toner image thereon through a fusing nip between a fusing roller member and a pressure roller member, and an image forming apparatus including the fuser. The image forming apparatus variously includes a copying machine, a printer, a facsimile machine, and a multifunction printer having integrated their functions.
2. Description of the Related Art
Conventional electrophotographic image forming apparatuses generally fix a toner image on a recording material by conveying, heating, and pressing the recording material having an unfixed toner image transferred thereon through a fusing nip between a fusing roller member configured to heat the unfixed toner image on the recording material and a pressure roller member making pressure-contact with the fusing roller member.
As a fuser of this kind, JP 2013-114058 A discloses a fuser which has a fusing roller member having an outer peripheral portion including an endless belt body. Further, JP 2013-114058 A discloses a configuration in which a guide is provided upstream of the fusing nip to stabilize the axial circumferential position of a belt body.
However, as illustrated in FIG. 11, in a conventional fuser as disclosed in JP 2013-114058 A, a gap is between a pressing member and a belt body at room temperature, the belt body is floated toward a pressing member upon start of warming up, and a radial circumferential position of the belt body is made unstable. The belt body having the unstable circumferential position is caused to make contact with a separating member disposed with a gap (e.g., 0.2 mm to 0.7 mm) therebetween. By contact of the belt body with a separating member, a contact trace remains on the belt body, and the contact trace disadvantageously generates uneven gloss upon fixing an image.
Further, in a configuration of the conventional fuser, in order to avoid the contact between the belt body and the separating member, considerable reduction of a relative adjustable width between the belt body and the separating member, or the like has been employed. However, the conventional fuser needs to be finely adjusted, needs a skilled engineer, and it takes a long time to adjust.
On the other hand, for avoidance only contact between the belt body and the separating member, increase of a gap between the belt body and the separating member is possible. However, when the gap between the belt body and the separating member is excessively increased, such a thin paper sheet as having an image with much toner (solid image) thereon cannot be separated and is wound around the belt body, and the separating member unfortunately does not function.